As black pigments, there have been conventionally used carbon black, perylene-based pigments and the like. Among these black pigments, carbon black has been most widely used because of its high tinctorial strength as well as an excellent blackness, an excellent acid resistance and an excellent weather fastness. However, carbon black has a very small particle size and a large bulk density and, therefore, tends to suffer from problems such as poor handling property and workability. Also, it may be difficult to use such carbon black in applications requiring a high electrical resistance, such as black matrix materials for liquid crystal color filters, because of a low electrical resistance thereof. Further, the carbon black may contain carcinogenic polycyclic condensation compounds and, therefore, has a problem concerning a safety.
Although the perylene-based pigments extensively used as fast pigments exhibit red-violet-brown-black colors in a solid state, the color tone thereof is not necessarily kept thermally stable (W. Herbst & K. Hunger “Industrial Organic Pigments”, VCH Press, pp. 467–480).
In order to improve the thermally unstable color tone of the perylene-based pigments, there have been proposed solid solution (mixed crystal) pigments composed of two diimide derivatives of perylene tetracarboxylic acid (Japanese Patent Application Laid-Open (KOKAI) Nos. 52-103450 and 57-139144 and Japanese Patent Publication (KOKOKU) No. 45-33552). However, these conventional black perylene-based pigments are deteriorated in blackness in spite of the high tinctorial strength thereof, so that there may be arise such a problem that the color tone thereof is readily changed when applying a mechanical shear force thereto. In the process described in Japanese Patent Publication (KOKOKU) No. 45-33552, the mixed crystal pigment is produced by dissolving raw compounds as a mixed crystal component in a solvent and then adding acids, etc. to the resultant solution, thereby precipitating the mixed crystal pigment.
An object of the present invention is to provide a black perylene-based pigment exhibiting an excellent blackness, an excellent heat resistance and an excellent weather fastness as well as a high safety, which is usable as black matrix pigments for liquid crystal color filters.